Increasing attention has been directed in recent years to minimizing release of gases and liquids (fluids), which are considered to be atmospheric pollutants, into the atmosphere. Such fluids may comprise gases, such as carbon dioxide, light hydrocarbons, hydrogen sulfide, sulfur oxides, nitrogen oxides, halogens and the like, along with or in aqueous or hydrocarbonaceous solutions, hydrocarbons, contaminated water, airborne particulates and the like. Many such materials are naturally present or are injected into subterranean formations during the production of hydrocarbons, the disposal of unwanted fluids and the like. When the production or disposal operations are completed, the wells used to penetrate such formations are typically cemented shut to prevent the release of these fluids into the air, overlying aquifers, or the like as leakage from wells penetrating subterranean formations.
Such formations may contain carbon dioxide having a density of less than 1 (one) as a result of naturally-occurring in situ carbon dioxide, from use of the well as a carbon dioxide injection/disposal well, from use of the well as either an injection or a production well in a carbon dioxide enhanced oil recovery process, and the like. There are a variety of reasons why subterranean formations containing carbon dioxide are desirably isolated so that the carbon dioxide does not flow into the atmosphere. The most commonly used technique for isolating such formations is plugging the wells penetrating the formation containing carbon dioxide. This is most commonly accomplished by cementing the wells shut.
Of continuing concern is whether the cement plug, or other plugging material, has fully plugged the well and whether it continues to block the flow of fluids, such as carbon dioxide, from flowing upwardly through the well into the atmosphere. Should leaks occur, the source of leaks into the atmosphere can be through or around the cement plugging, which cements the casing in place in the wellbore, or through or around the cement plugging the inside of the casing, which is typically used to case the well from the earth's surface to or through the carbon dioxide-bearing formation(s). Minute quantities of fluid leakage over long periods of time can erode the cement used to seal the well and result in larger leaks.
Various techniques have been used in the past for carbon dioxide measurement. These techniques include near infra red or other light absorption techniques and the like for the detection of carbon dioxide in flowing gas streams. However, such techniques are not effective for the detection of very minute quantities of carbon dioxide released on a continuing basis. Accordingly, an improved method for detecting fluid leakage from plugged wells has long been sought.